Electronics Fundamentals - Voltage, Current

 In this article, we will discuss the basics of electronics such as: Voltage, Current, and their rules and relationships. So, lets dive right into it!

A high voltage power line near New York City.

Watch full video below to understand the fundamentals of Voltage and Current:

VOLTAGE (represented by V or E):

    It is a value of energy i.e. the work done between two points required to move a unit of positive charge from the more negative point at a lower potential to the more positive point that has a higher potential, also known as Potential Difference or Electromotive Force (EMF). Unit of measurement is the volt (v), kilovolts (kV), millivolts (mV), microvolts (μV), megavolts (MV), or nanovolts (nV). One Joule (J) of work done in moving a coulomb (C) of charge through is 1V.


    The rate of flow of electric charge past a point. The unit of measurement of current is the ampere (A) or amperes or amp, milliamperes (mA), microamperes (μA), nanoamperes (nA), or picoamperes (pA). A current of 1A is the flow of 1C of charge per second. The direction of current is opposite to the of direction of charge.

Note: Current always flows through things and voltage is always applied to things. Oscilloscope is an important instrument that allows us to see voltages (or current) in a circuit as a function of time. In actual circuits we connect things together with wires (metallic conductors).

Important rules about voltage and current:
  • The sum of currents into a point (called node by engineers) in a circuit is equal to the sum of currents out because of conservation of charge. This is called Kirchhoff's Current Law (KCL). In a series circuit, the current is same everywhere.
Parallel Circuit connection.

  • Things hooked in parallel have the same voltage across them, which means the sum of the voltage drops from A to B from one path through the circuit is equal to the sum of voltage from another path. This is the voltage between a A and B. It can also be said that the sum of voltage drops around any closed circuit is zero, called Kirchhoff's Voltage Law (KVL).
  • Power (P) is equal to Voltage multiplied by Time, or P = VI. This can also be represented as energy/charge multiplied by charge/time. Unit of power is measured in Joule per second or Watts, so 1 Watt = 1 Joule per second. For Example: Current flowing through a 100 Watt lightbulb running on 120 volt is 0.834 amperes.
    • Power goes into heat, or mechanical work (in motors), or radiated energy (in lamps, transmitters), or stored energy (in batteries, capacitors, inductors), is managed as the heat load in complex systems design.